Neuronal Leucine Rich Repeat (NLRR) proteins were first identified from a mouse brain cDNA library and are encoded by a three-gene family in mammals (Taguchi et al., 1996; Taniguchi et al., 1996). They constitute a novel LRR protein family containing 11 or 12 LRRs, an immunoglobulin domain, and a type III fibronectin domain (Bormann et al., 1999; Fukamachi et al., 2001; Hayata et al., 1998). From their structural features, these glycosylated transmembrane proteins are postulated to play roles in cell adhesion, migration, morphogenesis or signaling. The regulated embryonic expression and cellular location of NLRR family proteins suggest important roles during development in the control of cell adhesion, movement or signaling (Haines et al., 2005), but their functions have remained elusive. NLRR-3 has been shown to have a role in potentiating EGFR signaling in response to low concentrations of EGF, probably by promoting association of EGFR and EGF in clathrin-coated pits and endosomes as there is no evidence for physical association with EGFR (Fukamachi et al., 2002). Endocytosis of EGFR has long been recognized as an attenuation mechanism, but several studies have revealed that endosomal complexes retain signaling potency and that EGFR internalization can even serve to amplify MAP kinase phosphorylation, and stimulate pathways leading to cell survival (Haugh et al., 1999a; Haugh et al., 1999b; Sato et al., 2001; Schoeberl et al., 2002; Wang et al., 2002)
NLRR-1 (as known as LRRN1) shares homology with NLRR-3, including complete conservation of the C-terminal endocytosis motif. NLRR-1 was identified as an early neuroectodermal developmental marker (Aubert et al., 2003) and has also been found in a subset of myogenic precursors during somite development (Haines et al., 2005), but its function remains unknown.
Data regarding expression of NLRR proteins in human disease states is limited, but in neuroblastoma, expression of NLRR-1, unlike NLRR-3, is significantly associated with short survival and poor prognostic factors (Hamano et al., 2004).
The epidermal growth factor receptor (EGFR) family comprises four closely related receptors (HER1/EGFR, HER2, HER3 and HER4). The EGFR family and associated ligands trigger a series of intracellular signaling events regulating cell proliferation, migration, differentiation and survival (Wells, 1999). EGFR pathway activation plays a fundamental role in malignancy, and recent advances in EGFR-targeted tumor therapy have highlighted several aspects of EGFR signaling and activation in tumorigenesis, including contributions of such factors as genomic amplification, protein expression, mutations, and downstream effectors (Dziadziuszko et al., 2006; Eberhard et al., 2005; Han et al., 2005; Lynch et al., 2004; Oliveira et al., 2006; Paez et al., 2004; Shepherd et al., 2005; Tsao et al., 2005).
Over-expression of the EGFR kinase, or its ligand TGF-alpha, is frequently associated with many cancers, including breast, lung, colorectal, ovarian, renal cell, bladder, head and neck cancers, glioblastomas, and astrocytomas, and is believed to contribute to the malignant growth of these tumors. A specific deletion-mutation in the EGFR gene (EGFRvIII) has also been found to increase cellular tumorigenicity. Activation of EGFR stimulated signaling pathways promote multiple processes that are potentially cancer-promoting, e.g. proliferation, angiogenesis, cell motility and invasion, decreased apoptosis and induction of drug resistance. Increased HER1/EGFR expression is frequently linked to advanced disease, metastases and poor prognosis. For example, in NSCLC and gastric cancer, increased HER1/EGFR expression has been shown to correlate with a high metastatic rate, poor tumor differ.
Intense research efforts are being made to develop anti-tumor agents that directly inhibit the kinase activity of the EGFR and antibodies that reduce EGFR kinase activity by blocking EGFR activation (de Bono J. S. and Rowinsky, E. K. (2002) Trends in Mol. Medicine 8:S19-S26; Dancey, J. and Sausville, E. A. (2003) Nature Rev. Drug Discovery 2:92-313). Several studies have demonstrated, disclosed, or suggested that some EGFR kinase inhibitors might improve tumor cell or neoplasia killing when used in combination with certain other anti-cancer or chemotherapeutic agents or treatments (e.g. Herbst, R. S. et al. (2001) Expert Opin. Biol. Ther. 1:719-732; Solomon, B. et al (2003) Int. J. Radiat. Oncol. Biol. Phys. 55:713-723; Krishnan, S. et al. (2003) Frontiers in Bioscience 8, e1-13; Grunwald, V. and Hidalgo, M. (2003) J. Nat. Cancer Inst. 95:851-867; Seymour L. (2003) Current Opin. Investig. Drugs 4(6):658-666; Khalil, M. Y. et al. (2003) Expert Rev. Anticancer Ther. 3:367-380; Bulgaru, A. M. et al. (2003) Expert Rev. Anticancer Ther. 3:269-279; Dancey, J. and Sausville, E. A. (2003) Nature Rev. Drug Discovery 2:92-313; Ciardiello, F. et al. (2000) Clin. Cancer Res. 6:2053-2063; and Patent Publication No: US 2003/0157104).
Erlotinib (e.g. erlotinib HCl, also known as TARCEVA® or OSI-774) is an orally available inhibitor of EGFR kinase. In vitro, erlotinib has demonstrated substantial inhibitory activity against EGFR kinase in a number of human tumor cell lines, including colorectal and breast cancer (Moyer J. D. et al. (1997) Cancer Res. 57:4838), and preclinical evaluation has demonstrated activity against a number of EGFR-expressing human tumor xenografts (Pollack, V. A. et al (1999) J. Pharmacol. Exp. Ther. 291:739). Erlotinib has demonstrated activity in clinical trials in a number of indications, including head and neck cancer (Soulieres, D., et al. (2004) J. Clin. Oncol. 22:77), NSCLC (Perez-Soler R, et al. (2001) Proc. Am. Soc. Clin. Oncol. 20:310a, abstract 1235), CRC (Oza, M., et al. (2003) Proc. Am. Soc. Clin. Oncol. 22:196a, abstract 785) and MBC (Winer, E., et al. (2002) Breast Cancer Res. Treat. 76:5115a, abstract 445; Jones, R. J., et al. (2003) Proc. Am. Soc. Clin. Oncol. 22:45a, abstract 180). In a phase III trial, erlotinib monotherapy significantly prolonged survival, delayed disease progression and delayed worsening of lung cancer-related symptoms in patients with advanced, treatment-refractory NSCLC (Shepherd, F. et al. (2004) J. Clin. Oncology, 22:14S (July 15 Supplement), Abstract 7022). In November 2004 the U.S. Food and Drug Administration (FDA) approved TARCEVA® for the treatment of patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) after failure of at least one prior chemotherapy regimen.
Despite the significant advancement in the treatment of cancer, improved therapies are still being sought.